Sill seal: Foam air seal vs. EPDM air seal
airfix
| Posted in General Questions on
I seen a few threads on sill sealing recently and I wanted to get in on the discussion. It’s a really important place to for air sealing. There are lots of recommendations for an EPDM gasket such as these:
http://conservationtechnology.com/building_gaskets.html
However (a phrase that I hear all too often) “around here everyone uses” a foam sill sealer such as these:
http://insulation.owenscorning.ca/builders/products/foamsealr.aspx
Those foam ones seem like they work as a capillary break but how are they at air sealing?
Steve
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Replies
They don't effectively air-seal. If you use sill-seal you need a bead of something at the concrete/wood intersection.
We use acoustical caulk. Super sticky and messy and many mentions of it on GBA. Anyone ever test how long it takes to dry? 20 years? 100?
I think it’s intended to NOT dry. I know it’s still just as nasty years later as the day it went in though. I’ve had to clean many a tool after dealing with the stuff. It does do a really good job maintaining a seal on things that move a little though!
Steve,
I personally believe that either option is fine. I opted for the cheaper Owens Corning style material with Acoustical Sealant above and below it and achieved a very tight enclosure. More importantly, I also taped the sheathing to our ICF foundation. (If it was concrete, then I would have used liquid flash.) I believe this step (exterior air-sealing) is more critical as I have seen 5/8" thick gaps between mudsills and concrete that no rubber gasket would fill.
It may sound like a lot, but I think it is worth taking the extra steps to air seal this part of the house (and area around trusses) as failing to do so can magnify heat loss due to the stack effect.
To echo Paul's point, acoustical sealant is a real pleasure to work with! :-)
Hi Steve -
I don't think that the evenness of the top of the foundation and the uneven point-loading of the mud sill (e.g. how compressed the sill sealer is at j-bolts compared to between) mean reliable air sealing from the sill sealer alone. Hence this product review (albeit dated) by Martin Holladay: https://www.greenbuildingadvisor.com/article/product-review-worlds-best-sill-seal.
Note in this blog the comments; some good perspective and a detail from Michael Chandler, one of the original GreenBuildingAdvisors.
Peter
Great info again. I'm not excited about using acoustic caulk and the potential mess every time someone touches it at each stage of the construction.
I've seen the product in the link that Peter presented before and Michael Chandlers comments seem to ring true about cost and grad school ideas. His detail of wrapping poly under the sill plate and over the top plate looks good but then I'm dealing with more tape to maintain the seal. Not sure I understand how the top plate wrap of poly over the sheathing helps with sealing.
Bottom line is if I go with the Owens Corning sill sealer I need to have a backup plan. Perhaps using the acoustic sealant. If I go with the much more expensive EDPM gasket I probably don't need a backup plan?
Steve
Steve,
In past discussions here, when objections to using acoustical sealant came up, a more benign alternative was suggested: Pro Clima HF.
https://www.greenbuildingadvisor.com/question/budget-friendly-alternative-to-pro-clima-contega-hf
I just found these two useful links. One of which is a "back yard" test on the foam vs the EPDM gasket. While the back yard testing is not totally applicable as most sill seals are not exposed to UV and it doesn't really address sealing it is a side by side look at the materials.
https://www.justneedspaint.com/house-gasket-durability/
https://www.justneedspaint.com/an-airtight-home-how-to-choose-and-install-sill-sealer-gasket/
Steve,
I don't think there is any doubt the gasket is a better product than sill-seal, but those backyard tests did nothing to prove that. Interior sill-seals are completely enclosed within the conditioned space, and those on exterior walls are pretty close to being too. Leaving scraps out on your lawn to test them is like leaving fibreglass batts or plywood in the same conditions. It just makes no sense.
Discussing this with my general he suggested that we use the Owens Corning sill seal but only install it under about 3" of the 2x6 sill plate. He suggested using a can of spray foam to foam the underside of the sill plate before it is bolted down and bolted down the foam has a chance to fully cure.
Does anybody have any comments on this?
It sounds like reinventing the wheel. Why not either use a gasket, or use sill -seal and run bead of sealant on either the interior or exterior of the joint between the sill and the foundation. That's how people generally do it.